The present invention relates to joints for sheet material and to methods of joining sheet material, and in particular to joints for sheet metal and to method of joining sheet metal.
It is known to join sheet metal components by welding an edge of one sheet metal component to the face of an adjacent sheet metal component, or by firstly bending over the end of one sheet metal component and welding the face of the bent over end of the first sheet metal component to the face of an adjacent sheet metal component. It is known that other types of bonding may be used for example brazing, soldering or adhesive.
It is also known to join sheet metal components by firstly bending over the end of one sheet metal component and riveting the face of the bent over end of the first sheet metal component to the face of an adjacent sheet metal component. It is also known that other types of mechanical attachment may be used for example nuts and bolts.
It is further known to join sheet metal components by firstly providing one or more projections from the edge of one of the sheet metal components, providing a corresponding number of slots through the adjacent sheet metal component and passing the projections on the first sheet metal component through the slats in the adjacent sheet metal component. It is known that the projections are then either bent over to abut the opposite face of the adjacent sheet metal component or the projections are twisted to prevent the projection withdrawing from the slot.
A problem with the welded, brazed or soldered joint is that these are hot joining processes which many require subsequent costly heat treatments of the sheet metal components.
A problem with the fold over projection joint or the twist projection joint is that they are not used in joints which are required to transmit or resist external loads. The fold over projection joint or the twist projection joint are normally used to simply maintain the relative positions of an assembly of sheet metal components. The fold over projection and twist projection have a tendency to unfold, untwist or deform such that the joint becomes loose.
FR1500021 discloses fastening a printed circuit board to a metallic sheet. The metallic sheet has projections which extend from the edge of the metallic sheet. The projections extend through slots in the printed circuit board and the projections are rotatable to fasten the printed circuit board onto the metallic sheet. The projection has a root which extends a predetermined distance from the edge of the metallic sheet into the main body of the metallic sheet. The printed circuit board is also spaced from the edge of the metallic sheet by other projections.
WO9812437 discloses joining metallic sheets. A first metallic sheet has projections which extend from the edge of the first metallic sheet. The projections extend through slots in the second metallic sheet and the projections has a twist tab which is to hold the second metallic sheet on the first metallic sheet. The projection has an alignment member which fits in the slot to relatively Locate the first and second metallic sheets. The twist tab is secured to the alignment member. Once the metallic sheets have been welded together the twist tab is broken off.
The present invention seeks to provide a twist projection joint for sheet metal which overcomes, or reduces, the above mentioned problems.
Accordingly the present invention provides a joint for joining a first ductile sheet to another structure comprising at least one projection on an edge of the first ductile sheet, the at least one projection being rotatable about an axis, the axis being arranged in the plane of the first ductile sheet and in a plane extending perpendicularly to the edge of the first ductile sheet, at least one slot extending through the other structure, the at least one projection extending through the at least one slot in the other structure, the at least one projection being rotated such that the at least one projection is in a plane arranged at angle to the plane of the first ductile sheet and the at least one projection abuts the other structure at both sides of the slot to clamp the other structure between the edge of the first ductile sheet and the at least one projection, the at least one projection comprises a root portion which extends from the projection into the main body of the first ductile sheet, the root portion extends for a predetermined distance from the edge of the first ductile sheet into the main portion of the first ductile sheet, characterised in that there is at least one additional projection extending from the edge of the first ductile sheet adjacent the at least one projection, there is at least one second additional projection extending from the edge of the first ductile sheet adjacent the at least one projection, the first and second additional projection extending into the at least one slot in the other structure to relatively locate the first ductile sheet and other structure, the first and second additional projections are on opposite sides of the projection.
Preferably the first ductile sheet comprises a plurality of projections on the edge of the first ductile sheet, a corresponding number of slots through the other structure, each projection extends through a corresponding one of the slots through the other structure, each projection being rotated such that the projection is arranged at an angle to the plane of the first ductile sheet to clamp the other structure between the edge of the first ductile sheet and the projection.
Preferably apertures are arranged at the sides of the root portion.
Preferably the at least one slot through the other structure comprises stub-slots extending perpendicularly from the centre of the at least one slot and ramps extending from the slot to the sub-slots to allow rotation of the root portion about the axis.
Preferably the ramps are arranged to define pawls with the ends of the slots to prevent rotation of the root portion in the direction to loosen the joint.
Preferably the additional projection extends from the to edge of the first ductile sheet by a distance equal to or less than the thickness of the second ductile sheet.
Preferably the second additional projection extends from the edge of the first ductile sheet by a distance equal to or less than the thickness of the second ductile sheet.
Preferably each projection is symmetrical about a plane extending perpendicularly to the edge of the first ductile sheet.
Preferably each root portion is symmetrical about a plane extending perpendicularly to the edge of the first ductile sheet.
Preferably the other structure comprises a second ductile sheet.
Preferably the joint comprises a third ductile sheet, at least one slot extending through the third ductile sheet, the at least one projection extending through the at least one slot in the third ductile sheet, the third ductile sheet being clamped between the edge of the first ductile sheet and the second ductile sheet.
Preferably the at least one projection is rotated such that the at least one projection is in a plane arranged perpendicularly to the plane of the first ductile sheet.
Preferably the ductile sheets are metallic sheets. Preferably the metallic sheets are stainless steel sheets or nickel alloy sheets.
The present invention also provides a method of joining a first ductile sheet to another structure comprising forming at least one projection on an edge of the first ductile sheet, the at least one projection being rotatable about an axis, the axis being arranged in the plane of the first ductile sheet and in a plane extending perpendicularly to the edge of the first ductile sheet, forming at least one slot extending through the other structure, inserting the at least one projection through the at least one slot in the other structure, rotating the at least one projection around the axis such that the at least one projection is in a plane arranged at angle to the plane of the first ductile sheet and such that the at least one projection abuts the other structure at both sides of the slot to clamp the other structure between the edge of the first ductile sheet and the at least one projection, forming a root portion on the at least one projection which extends from the projection into the main body of the first ductile sheet, the root portion extends for a predetermined distance from the edge of the first ductile sheet into the main portion of the first ductile sheet characterised by, forming at least one additional projection extending from the edge of the first ductile sheet adjacent the at least one projection, forming at least one second additional projection extending from the edge of the first ductile sheet adjacent the at least one projection, inserting the first and second additional projections into the at least one slot in the other structure to relatively locate the first ductile sheet and the other structure, the first and second additional projections are on the opposite sides of the projection.
Preferably the method comprises forming a plurality of projections on the edge of the first ductile sheet, forming a corresponding number of slots through the other structure, inserting each projection through a corresponding one of the slots through the other structure, rotating each projection about the axis such that the projection is arranged at an angle to the plane of the first ductile sheet to clamp the other structure between the edge of the first ductile sheet and the projection.
Preferably the method comprises forming apertures through the first ductile sheet at the sides of the root portion.
Preferably the method comprises forming sub-slots extending perpendicularly from the centre of the at least one slot and forming ramps extending from the slot to the sub-slots to allow rotation of the root portion about the axis.
Preferably the additional projection extends from the edge of the first ductile sheet by a distance equal to or less than the thickness of the second ductile sheet.
Preferably the second additional projection extends from the edge of the first ductile sheet by a distance equal to or less than the thickness of the second ductile sheet.
Preferably the method comprises forming each projection symmetrically about a plane extending perpendicularly to the edge of the first ductile sheet.
Preferably the method comprises forming each root portion symmetrically about a plane extending perpendicularly to the edge of the first ductile sheet.
Preferably the method comprises forming the at least one projection by laser cutting.
Preferably the method comprises forming the at least one slot by laser cutting.